U.S. patent application number 10/936796 was filed with the patent office on 2005-03-17 for method and apparatus for multiphoton-absorption exposure wherein exposure condition is changed with depth of convergence position.
This patent application is currently assigned to FUJI PHOTO FILM CO., LTD.. Invention is credited to Tani, Takeharu.
Application Number | 20050057736 10/936796 |
Document ID | / |
Family ID | 34269883 |
Filed Date | 2005-03-17 |
United States Patent
Application |
20050057736 |
Kind Code |
A1 |
Tani, Takeharu |
March 17, 2005 |
Method and apparatus for multiphoton-absorption exposure wherein
exposure condition is changed with depth of convergence
position
Abstract
A multiphoton-absorption exposure apparatus for exposing a
multiphoton absorption material by applying light to the
multiphoton absorption material so that the light converges at a
predetermined convergence position, in which an exposure-condition
control unit is provided for changing an exposure condition so that
optical reactions are more likely to occur when the predetermined
convergence position is located deeper in the multiphoton
absorption material.
Inventors: |
Tani, Takeharu;
(Kanagawa-ken, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
FUJI PHOTO FILM CO., LTD.
|
Family ID: |
34269883 |
Appl. No.: |
10/936796 |
Filed: |
September 9, 2004 |
Current U.S.
Class: |
355/55 |
Current CPC
Class: |
G03F 7/70375 20130101;
G03B 27/52 20130101 |
Class at
Publication: |
355/055 |
International
Class: |
G03B 027/52 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2003 |
JP |
319735/2003 |
Claims
What is claimed is:
1. A multiphoton-absorption exposure method for exposing a
multiphoton absorption material, comprising the steps of: (a)
changing an exposure condition for exposing said multiphoton
absorption material to light so that optical reactions are more
likely to occur when the light converges at deeper positions in the
multiphoton absorption material; and (b) applying said light to
said multiphoton absorption material so that the light converges at
a predetermined convergence position in the multiphoton absorption
material under said exposure condition changed in said step
(a).
2. A multiphoton-absorption exposure method according to claim 1,
wherein said exposure condition includes at least one of an
exposure intensity, an exposure time, and a wavelength of said
light.
3. A multiphoton-absorption exposure method according to claim 2,
wherein at least one of said exposure intensity and said exposure
time is controlled by modulating said light with a light
modulator.
4. A multiphoton-absorption exposure method according to claim 1,
wherein said light is pulsed light emitted from a pulse laser.
5. A multiphoton-absorption exposure method according to claim 1,
wherein said multiphoton absorption material is an
ultraviolet-curing resin.
6. A multiphoton-absorption exposure method according to claim 1,
wherein said multiphoton absorption material is three-dimensionally
exposed by controlling said convergence position in three
directions including a depth direction and two directions which are
different from the depth direction.
7. A multiphoton-absorption exposure apparatus for exposing a
multiphoton absorption material, comprising: an exposure-condition
control unit which changes an exposure condition for exposing said
multiphoton absorption material to light so that optical reactions
are more likely to occur when the light converges at deeper
positions in the multiphoton absorption material; and an exposure
unit which applies said light to said multiphoton absorption
material so that the light converges at a predetermined convergence
position under said exposure condition changed by said
exposure-condition control unit.
8. A multiphoton-absorption exposure apparatus according to claim
7, wherein said exposure condition includes at least one of an
exposure intensity, an exposure time, and a wavelength of said
light.
9. A multiphoton-absorption exposure apparatus according to claim
8, further comprising a light modulator which modulates said light
so as to control at least one of said exposure intensity and said
exposure time.
10. A multiphoton-absorption exposure apparatus according to claim
7, further comprising a pulse laser which emits pulsed light as
said light.
11. A multiphoton-absorption exposure apparatus according to claim
7, further comprising a three- dimensional-exposure control unit
which controls said convergence position in three directions
including a depth direction and two directions which are different
from the depth direction, for realizing three-dimensional exposure
of said multiphoton absorption material.
12. A multiphoton-absorption exposure apparatus according to claim
11, wherein said three-dimensional-exposure control unit includes a
three-axis movement table for three-dimensionally moving said
multiphoton absorption material with respect to said light.
13. A multiphoton-absorption exposure apparatus according to claim
7, further comprising a storage unit which stores a table defining
exposure conditions for possible values of the depth of said
predetermined convergence position, and said exposure-condition
control unit determines said exposure condition for exposing said
multiphoton absorption material, by referring to said table based
on an actual value of the depth of said predetermined convergence
position.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a multiphoton-absorption
exposure method and a multiphoton-absorption exposure apparatus for
exposing a recording medium or the like by using multiphoton
absorption (such as two-photon absorption), which is known as one
of the nonlinear optical effects.
[0003] 2. Description of the Related Art
[0004] The following documents (1) to (4) disclose information
related to the present invention.
[0005] (1) U.S. Patent Laid-Open No. 20010001607
[0006] (2) U.S. Patent Laid-Open No. 20030052311
[0007] (3) "Three-dimensional Microfabrication with
Two-photon-absorbed Photopolymerization" by S. Maruo et al.,
(OPTICS LETTERS, Vol. 22, No. 2, pp.132-134, Jan. 15, 1997)
[0008] (4) "Two-photon-absorption Optical-fabrication with a
Micro-lens Array" by Y. Adachi et al., (Extended Abstracts of the
50th Spring Meeting of the Japan Society of Applied Physics and
Related Societies, 27p-YN-4, March 2003)
[0009] Although only one photon is absorbed in most light
absorption processes occurring in materials, exposure to high-power
light such as ultrashort pulse laser light can cause the so-called
multiphoton absorption, in which two or more photons are
simultaneously absorbed. For example, the amount of energy which a
material receives in the two-photon absorption is twice the amount
of energy which a material receives in the single-photon
absorption, and reactions of two-photon absorption caused by
exposure to high-power light having a wavelength 21 (in which the
photon energy is half of that in the light having a wavelength 1)
to a material which primarily absorbs the light having the
wavelength 1 are equivalent to reactions caused by exposure to the
light having the wavelength 1.
[0010] The probability of multiphoton absorption increases in
proportion to the photon density. Therefore, when converging light
is applied to a multiphoton absorption material, it is possible to
selectively cause multiphoton absorption only in the vicinity of a
convergence position of the converging light, where the photon
density is maximized at the convergence position. Thus, when a
recording material is realized by a material in which a change in
the phase, the refractive index, the chemical state, or the like is
caused by multiphoton absorption, it is possible to record
information in a plurality of layers in the recording material by
exposing the recording material to converging light, and
specifically by scanning each layer with the converging light and
shifting the depth of the convergence position to the next layer in
order to scan the next layer. The aforementioned document (1)
discloses an example of an apparatus which records information by
scanning a multiphoton absorption material with converging light
for exposure as mentioned above.
[0011] In other disclosed methods, three-dimensional optical
molding of a multiphoton absorption material in which a
photopolymerization reaction occurs is performed by
three-dimensionally exposing the multiphoton absorption material to
converging light, where the above-mentioned fact that multiphoton
absorption is caused only in the vicinity of the convergence
position of the converging light is utilized. The aforementioned
documents (3) and (4) disclose examples of apparatuses for
performing three-dimensional optical molding of a multiphoton
absorption material as mentioned above. In addition, the document
(4) also discloses a method for splitting a single laser beam into
a plurality of laser beams by use of a microlens array, and
concurrently molding a plurality of three-dimensional structures by
use of the plurality of laser beams.
[0012] Further, the document (2) discloses examples of preferable
multiphoton absorption materials which have great two-photon
absorption cross sections. For example, when light-curing resin is
mixed into the multiphoton absorption materials, such multiphoton
absorption materials become applicable to optical molding.
[0013] However, conventionally, when three-dimensional, information
recording, optical molding, and the like are performed by exposing
multiphoton absorption materials as mentioned above, the
probability of occurrence of optical reactions varies with the
depth of the exposure in the multiphoton absorption materials.
Therefore, the exposure becomes insufficient or excessive.
SUMMARY OF THE INVENTION
[0014] The present invention has been developed in view of the
above circumstances.
[0015] The object of the present invention is to provide a
multiphoton-absorption exposure method and a multiphoton-absorption
exposure apparatus which realize satisfactory exposure regardless
of the depth of the exposure in a multiphoton absorption
material.
[0016] (I) In order to accomplish the above first object, the first
aspect of the present invention is provided. According to the first
aspect of the present invention, there is provided a
multiphoton-absorption exposure method for exposing a multiphoton
absorption material. The multiphoton-absorption exposure method
comprises the steps of: (a) changing an exposure condition for
exposing the multiphoton absorption material to light so that
optical reactions are more likely to occur when the light converges
at deeper positions in the multiphoton absorption material; and (b)
applying the light to the multiphoton absorption material so that
the light converges at a predetermined convergence position in the
multiphoton absorption material under the exposure condition
changed in the step (a).
[0017] Preferably, the multiphoton-absorption exposure method
according to the first aspect of the present invention may also
have one or any possible combination of the following additional
features (i) to (iv).
[0018] (i) The exposure condition may include at least one of an
exposure intensity, an exposure time, and a wavelength of the
light.
[0019] (ii) In the multiphoton-absorption exposure apparatus having
the feature (i), at least one of the exposure intensity and the
exposure time may be controlled by modulating the light with a
light modulator.
[0020] (iii) The light may be pulsed light emitted from a pulse
laser.
[0021] (iv) The multiphoton absorption material may be an
ultraviolet-curing resin.
[0022] (v) The multiphoton absorption material may be
three-dimensionally exposed by controlling the convergence position
in three directions including a depth direction and two directions
which are different from the depth direction.
[0023] (II) In order to accomplish the above second object, the
second aspect of the present invention is provided. According to
the second aspect of the present invention, there is provided a
multiphoton-absorption exposure apparatus for exposing a
multiphoton absorption material. The multiphoton-absorption
exposure apparatus comprises: an exposure-condition control unit
which changes an exposure condition for exposing the multiphoton
absorption material to light so that optical reactions are more
likely to occur when the light converges at deeper positions in the
multiphoton absorption material; and an exposure unit which applies
the light to the multiphoton absorption material so that the light
converges at a predetermined convergence position under the
exposure condition changed by the exposure-condition control
unit.
[0024] Preferably, the multiphoton-absorption exposure apparatus
according to the second aspect of the present invention may also
have one or any possible combination of the aforementioned
additional feature (i) and the following additional features (vi)
to (x).
[0025] (vi) The multiphoton-absorption exposure apparatus having
the aforementioned feature (i) may further comprise a light
modulator which modulates the light so as to control at least one
of the exposure intensity and the exposure time.
[0026] (vii) The multiphoton-absorption exposure apparatus
according to the second aspect of the present invention may further
comprise a pulse laser which emits pulsed light as the light.
[0027] (viii) The multiphoton-absorption exposure apparatus
according to the second aspect of the present invention may further
comprise a three-dimensional-exposure control unit which controls
the convergence position in three directions including a depth
direction and two directions which are different from the depth
direction, for realizing three-dimensional exposure of the
multiphoton absorption material.
[0028] (ix) In the multiphoton-absorption exposure apparatus having
the above feature (viii), the three-dimensional-exposure control
unit may include a three-axis movement table for
three-dimensionally moving the multiphoton absorption material with
respect to the light.
[0029] (x) The multiphoton-absorption exposure apparatus according
to the second aspect of the present invention may further comprise
a storage unit which stores a table defining exposure conditions
for possible values of the depth of the predetermined convergence
position, and the exposure-condition control unit may determine the
exposure condition for exposing the multiphoton absorption
material, by referring to the table based on an actual value of the
depth of the predetermined convergence position.
[0030] (III) The advantages of the present invention are explained
below.
[0031] Through the present inventor's research, it is found that
the probability of occurrence of optical reactions varies with the
depth in the multiphoton absorption material since the exposure
light is scattered or absorbed by the multiphoton absorption
material before the exposure light reaches the convergence
position, and the convergence spot spreads due to aberration. The
degree of the above scattering or absorption and the spread of the
convergence spot increase with the depth. However, conventionally
the exposure condition is fixed regardless of the depth of the
convergence position. Therefore, when the convergence position is
located deeper, the optical reactions are less likely to occur.
[0032] In view of the above findings, in the multiphoton-absorption
exposure method according to the first aspect of the present
invention, the exposure condition is changed so that optical
reactions are more likely to occur when the predetermined
convergence position is located deeper in the multiphoton
absorption material. Therefore, it is possible to compensate for
the difference in the probability of occurrence of the above
scattering, absorption, and the like, and substantially equalize
the probability of occurrence of optical reactions at all
depths.
[0033] In addition, the multiphoton-absorption exposure apparatus
according to the second aspect of the present invention comprises
an exposure-condition control unit which changes the exposure
condition so that optical reactions are more likely to occur when
the predetermined convergence position is located deeper in the
multiphoton absorption material. Therefore, it is possible to
automatically compensate for the difference in the probability of
occurrence of the above scattering or absorption, and substantially
equalize the probability of occurrence of optical reactions at all
depths.
[0034] Further, when the multiphoton-absorption exposure apparatus
according to the second aspect of the present invention comprises a
storage unit which stores a table defining exposure conditions for
possible values of the depth of the predetermined convergence
position, and the exposure-condition control unit determines the
exposure condition by referring to the table based on an actual
value of the depth of the predetermined convergence position, it is
possible to make the exposure condition appropriate at all times,
and realize more stable exposure.
DESCRIPTION OF THE DRAWINGS
[0035] FIGURE is a schematic side view of a multiphoton-absorption
exposure apparatus according to an embodiment of the present
invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0036] An embodiment of the present invention is explained in
detail below with reference to the drawing.
[0037] First, an image exposure apparatus according to the
embodiment of the present invention is explained below.
[0038] FIGURE is a schematic side view of a multiphoton-absorption
exposure apparatus according to an embodiment of the present
invention. In the example of FIGURE, the multiphoton-absorption
exposure apparatus realizes a three-dimensional optical molding
apparatus. As illustrated in FIGURE, the multiphoton-absorption
exposure apparatus according to the present embodiment comprises a
pulse laser 11, a mirror 12, a condensing lens 13, a resin vessel
15, and a three-axis movement table 16. The pulse laser 11 emits
pulsed light 10 as exposure light as illustrated in FIGURE. The
mirror 12 bends the optical path of the pulsed light 10 by 90
degrees. The condensing lens 13 converges the pulsed light 10 after
the pulsed light 10 is reflected by the mirror 12. A liquid resin
14 for optical molding (hereinafter referred to as the
optical-molding resin) is pooled in the resin vessel 15, which is
fixed on the three-axis movement table 16. The three-axis movement
table 16 can linearly move the resin vessel 15 in each of the x, y,
and z directions in very small steps.
[0039] In addition, the multiphoton-absorption exposure apparatus
of FIGURE further comprises a light modulator 20, a modulator
driving circuit 21, and a control unit 22. The light modulator 20
is inserted in the optical path of the pulsed light 10 between the
pulse laser 11 and the mirror 12, and is, for example, an
acoustic-optical light modulator (AOM). The modulator driving
circuit 21 drives the light modulator 20. The control unit 22
controls the operations of the modulator driving circuit 21 and the
movement of the three-axis movement table 16, and is realized by,
for example, a computer system.
[0040] The pulse laser 11 is, for example, a Ti:sapphire laser. In
this embodiment, the pulse laser 11 has an average output power of
1 W, an oscillation wavelength of 780 nm, a pulse repetition
frequency of 82 MHz, and a pulse width of 100 fs (femtoseconds). In
addition, the condensing lens 13 has a numerical aperture (NA) of
0.7 and a magnification power of 100. Further, the optical-molding
resin 14 is an ultraviolet-curing resin in which two-photon
absorption occurs, e.g., an epoxy resin. A concrete example of such
a resin is SCR-701 (available from D-MEC Ltd. in Japan), which is
disclosed in the aforementioned document (2).
[0041] Hereinbelow, the operations of exposure performed by the
above multiphoton-absorption exposure apparatus are explained. In
order to perform exposure for three-dimensional optical molding,
first, the position, in the z direction, of the resin vessel 15
containing the optical-molding resin 14 is maintained by
controlling the movement of the three-axis movement table 16. In
this situation, the pulse laser 11 is driven so that the pulsed
light 10 is emitted. Then, the control unit 22 controls the
operation of the modulator driving circuit 21 based on a signal Si
which indicates a three-dimensional shape to be molded, so that,
for example, on-off modulation of the pulsed light 10 is
performed.
[0042] The modulated pulsed light 10 is reflected by the mirror 12,
and then the condensing lens 13 makes the pulsed light 10 converge
inside the optical-molding resin 14. The resin vessel 15 containing
the optical-molding resin 14 is moved in the x and y directions in
very small steps while maintaining the position of the resin vessel
15 in the z direction. Thus, the entire x-y plane at a position in
the z direction is two-dimensionally scanned with and exposed to
the modulated pulsed light 10. As mentioned before, the pulsed
light 10 has the pulse width as short as 100 fs, and therefore the
photon density becomes extremely high in the vicinity of and at the
convergence position F of the pulsed light 10. Thus, only in the
vicinity of and at the convergence position F of the pulsed light
10, two-photon absorption occurs as mentioned before,
photopolymerization occurs as in the case of absorption of
ultraviolet light having a wavelength of 390 nm (=780/2 nm) by the
optical-molding resin, and the optical-molding resin 14 is
cured.
[0043] When the above two-dimensional scanning with the pulsed
light 10 is completed, the resin vessel 15 containing the
optical-molding resin 14 is moved in the z direction by a very
small amount which is predetermined, and two-dimensional scanning
with and exposure to the modulated pulsed light 10 are performed at
the position moved in the z direction as performed before the
convergence position is moved in the z direction. Thereafter,
movement of the resin vessel 15 in the z direction and
two-dimensional scanning with the pulsed light 10 are repeated, and
finally three-dimensional scanning and exposure of the
optical-molding resin 14 is realized. Thus, the optical-molding
resin 14 is cured so as to form the three-dimensional shape
corresponding to the signal S1, i.e., a desired shape is molded
from the optical-molding resin 14.
[0044] Instead of the on-off modulation of the pulsed light 10
based on the signal Si, the light modulator 20 can continuously
change the transmittance through the light modulator 20, for
example, within the range from 0 to 100%, and the control unit 22
controls the operation of the modulator driving circuit 21
according to the position of the three-axis movement table 16 in
the z direction so that the transmittance through the light
modulator 20 increases with the depth of the convergence position F
in the optical-molding resin 14 (measured from the incident surface
of the optical-molding resin 14, through which the pulsed light 10
enters the optical-molding resin 14).
[0045] As explained before, the pulsed light 10 as the exposure
light can suffer from scattering and absorption by the multiphoton
absorption material before the pulsed light 10 reaches the
convergence position F, and the convergence spot spreads due to
aberration. In addition, the probability of occurrence of such
phenomenons increases with the depth of the convergence position F.
Therefore, if the exposure condition is fixed regardless of the
depth of the convergence position F, the desired optical reactions
are less likely to occur when the depth of the convergence position
F increases.
[0046] On the other hand, in the multiphoton-absorption exposure
apparatus according to the present embodiment, the intensity of the
light which passes through the light modulator 20, i.e., the
exposure intensity, is increased with the depth of the convergence
position F. Therefore, it is possible to compensate for the
difference in the probability of occurrence of the scattering,
absorption, and the like, and substantially equalize the
probability of occurrence of optical reactions at all depths in the
optical-molding resin 14. Thus, it is possible to realize
satisfactory exposure without insufficiency or excess at all times.
This advantage of the present invention is explained in further
detail below, where the present invention is compared with
comparison examples (1 and 2), to which the present invention is
not applied.
[0047] First, in the comparison example 1, the optical-molding
resin 14 is three-dimensionally exposed under a fixed exposure
condition which optimizes the exposure, for example, in the
vicinity of the incident surface of the optical-molding resin 14.
For example, this exposure condition is that the average output
power of the exposure light is 10 mW, and the illumination time for
curing each point is 1 ms (millisecond). In this case, the present
inventor has observed insufficient exposure when the depth of the
convergence position F increases. For example, when the depth of
the convergence position F exceeds 300 micrometers, the
optical-molding resin 14 cannot be cured.
[0048] Next, in the comparison example 2, the optical-molding resin
14 is three-dimensionally exposed under a fixed exposure condition
which optimizes the exposure, for example, at the depth of 300
micrometers in the optical-molding resin 14. For example, this
exposure condition is that the average output power of the exposure
light is 20 mW, and the illumination time for curing each point is
1 ms (millisecond). In this case, when the convergence position F
is near to the incident surface of the optical-molding resin 14,
the exposure becomes excessive, and the resolution deteriorates or
the optical-molding resin 14 boils due to local heat
absorption.
[0049] On the other hand, the present inventor has confirmed that
satisfactory exposure is enabled regardless of the depth of the
convergence position F in the embodiment of the present invention
when the illumination time for curing each point (i.e., the
exposure time) is maintained at 1 ms (millisecond), and the
intensity of the light which passes through the light modulator 20
is changed, for example, for every 50 .mu.m change in the depth of
the convergence position F so that the output power of the exposure
light is changed within the range of 10 to 50 mW. Specifically, the
present inventor has confirmed that satisfactory exposure without
insufficiency or excess is enabled in the region of the
optical-molding resin 14 from the vicinity of the incident surface
to the depth of 1 mm.
[0050] Alternatively, the present inventor has also confirmed that
satisfactory exposure is enabled regardless of the depth of the
convergence position F in the embodiment of the present invention
when the intensity of the light which passes through the light
modulator 20 is maintained at the average output power of 10 mW,
and the illumination time for curing each point (i.e., the exposure
time) is changed, for example, for every 50 .mu.m change in the
depth of the convergence position F within the range of 1 ms to 100
ms.
[0051] As understood from the above explanations, the
aforementioned exposure-condition control unit in the second aspect
of the present invention, which changes an exposure condition so
that optical reactions are more likely to occur when the
predetermined convergence position is located deeper in the
multiphoton absorption material, is realized by the light modulator
20, the modulator driving circuit 21, and the control unit 22.
[0052] It is possible to obtain values of the exposure time or the
output power of the exposure light (i.e., the exposure intensity)
at respective convergence positions F which are appropriate for
realizing the above change in the exposure condition, based on
experiments or experiences. In addition, it is convenient that the
appropriate values of the exposure time or the output power of the
exposure light are stored in advance in a storage in correspondence
with the respective convergence positions F in the form of a table
so that the appropriate values can be read out from the table and
set when exposure is actually performed. In this case, it is
possible to make the exposure condition appropriate at all times,
and realize more stable exposure. Further, after the appropriate
values of the exposure time or the output power of the exposure
light at the respective convergence positions F are obtained based
on the experiments or experiences, additional values of the
exposure time or the output power of the exposure light
interpolating between the above appropriate values based on the
experiments or experiences can be obtained by calculation, so that
appropriate values of the exposure time or the output power of the
exposure light can be obtained more finely.
[0053] Further, it is possible to change the wavelength of the
exposure light, instead of the exposure time or the output power of
the exposure light (the exposure intensity), according to the
convergence position. The efficiency of the multiphoton absorption
reactions varies with the wavelength of the exposure light.
Therefore, when the wavelength of the exposure light is changed so
that the efficiency of the multiphoton absorption reactions
increases with the depth of the convergence position F in the
multiphoton absorption material, it is possible to substantially
equalize the probability of occurrence of optical reactions at all
depths in the multiphoton absorption material. Since the
oscillation wavelength of the aforementioned Ti:sapphire laser can
be changed in the range about 700 to 1,000 nm, it is preferable to
use the Ti:sapphire laser in the case where the wavelength of the
exposure light is changed according to the present invention.
[0054] Although the multiphoton-absorption exposure apparatus
realizes a three-dimensional optical molding apparatus in the above
embodiment, the present invention can also be applied to
multiphoton-absorption exposure apparatuses realizing information
recording apparatuses which perform multilayer recording in optical
disks or the like. In such cases, advantages similar to those of
the above embodiment are obtained.
[0055] In addition, all of the contents of the Japanese patent
application No. 2003-319735 are incorporated into this
specification by reference.
* * * * *